Tone detection plays a crucial role in telephony applications.  Tone detectors are required for echo cancellers, to prevent incorrect adaptation, causing replication of echo.  They can be used in noise reduction algorithms, and in the state machines of IPBX and modem software. Tone detectors are also used in many communications protocols to decode information signals encoded using tones, such as alarm panel protocols, telephony protocols, and radio protocols.

Utilizing the FFT for the detection of tone would be a practical approach, however, for tone detection with just a few target frequencies, the full spectrum needs not to be evaluated. The Goertzel algorithm provide a computational efficient approach to determining the real and imaginary frequency components of a target frequency. With proper thresholding and timing requirements, the tone detection algorithm will not produce false alarms on quasi-stationary signals, such as voiced speech.

VOCAL’s Tone Detection software is incorporated as part of its VoIP, Data, Fax and Voice Quality Enhancement software solutions, but is also available as a standalone module.


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